Down hole tools have been employed to obtain formation fluid samples. In certain prior art apparatus, fluids have been analyzed by flowing them through a fluid analyzing module of the tool. Fluid conditions, such as the permeability of the fluid through the formation, as well as the pressure, volume, temperature and acidity of the fluid, may be measured with such apparatus.
Such a down hole tool may include several modules, including but not limited to a probe module, a hydraulic module, a fluid analysis module, a pump-out module, a flow control module, one or more sample container modules, and a power module. The tool is typically suspended by a wire and lowered into a borehole. In certain embodiments, the tool may include a pair of packer modules mounted on the tool to isolate and position the probe and any other module at a certain location within the borehole. Fluid removed from the tool may be delivered to a fluid analysis module for analyzing. As used herein, “borehole” shall describe any generally tubular structure or open hole in which a device or tool is capable of being lowered into and anchored or otherwise secured within the passageway of the tubular structure or open hole. The definition of “borehole” shall include a structure adapted for oil exploration and shall also include any other structure not adapted for oil exploration, such as a pipe used to convey fluid.
Such tools may employ probe modules having two probes. By providing two probes, either through two single-probe modules or through a dual-probe module, pressure communication between adjacent formations may be monitored during an interference test. In addition, this configuration may also provide for in-situ verification of gauge quality and for redundancy in difficult conditions.